Iris controlled slot coupler



Aug. 9, 1966 F. J. GOEBELS, JR

IRIS CONTROLLED SLOT COUPLER Filed March 14, 1963 Arum 5% United StatesPatent 3,266,043 IRIS CONTROLLED SLOT COUPLER Frank J. Goebeis, .lxn,Los Angeles, Calif., assignor to Hughes Aircraft Company, Culver City,Calif, 21 corporation of Delaware Filed Mar. 14, 1963, Ser. No. 265,25619 Claims. (Cl. 343-768) The present invention relates generally tocoupling devices for microwaves and more particularly to slot couplersutilizing irises for controlling slot radiation.

It is well known that slots disposed along the longitudinal centerlineof a stadard rectangular waveguide do not radiate. However, a physicallyasymmetric iris disposed in the waveguide in a plane transverse to theslot creates a modal asymmetry which distorts the current flow in thevicinity of the slot causing it to radiate. Thus, by varying the degreeof this asymmetry, the characteristics of the slot radiation may becontrolled. In one known device, metallic plates are used to form suchan iris for controlling slot radiation. Here, the iris similarlydisposed in the transverse plane extends outwardly through the narrowWalls of the waveguide and permits mechanical movement in this plane.Thus, by displacing the iris asymmetrically in the waveguide, a currentdistribution other than zero may be established in the vicinity of theslot and, as a result, the slot radiates. A full discussion is set forthin the US. Letters Patent No. 2,946,057 issued to Howard E. Shanks onJuly 19, 1960. However, with this device, mechanical adjustments arenecessary to control the radiation characteristics of the slot.

In another known device, the two plates of a resonant iris are formedfrom ferrite material and subjected to a static magnetic field providedby externally mounted electromagnets. In this device, the iris ispermanently positioned and the slot radiation controlled by anappropriate adjustment of the magnetic field intensity in one platerelative to the other. Here, the plates act as induct-ive elements whichdistort the otherwise symmetrical current distribution in the vicinityof the centered slot causing it to radiate. A complete description iscontained in US. Letters Patent No. 2,946,056 to Howard E. Shanks, datedJuly 19, 1960. However, in this device, electromagnets are required.

In brief, the slot coupler of the present invention comprises a centeredslot cut in the broad wall of a rectangular waveguide and asemiconductor iris, or irises, mounted transversely in the waveguidenear the slot. Nonlinear semiconductor devices are used to form the irisand may be either variable capacitance diodes known as varactor diodesor plate-like partitions of semiconductor material. By differentiallybiasing the semiconductor devices accordingly, a modal asymmetry iscreated distorting the current flow in the vicinity of the slot andcausing it to radiate in a predictable fashion.

Accordingly, it is an object of the present invention to provide an iriscontrolled slot coupler with which the radiation characteristics of aslot or slot array so equipped may be controlled electronically.

It is another object of the invention to provide an iris controlled slotcoupler possessing a faster response time than prior iris controlledslots.

It is still another object of the invention to provide an iriscontrolled slot coupler wherein lower driving power is required thanthat norm-ally needed for ferrite irises.

It is a further object to provide an iris controlled slot coupler thatis particularly applicable in slot arrays and still allows suitableisolation between the control circuitry of consecutive irises.

Another object is to provide a simple, compact iris controlled slotcoupler in which a dry cell battery may be used as a source of drivingpower.

In accordance with these and other features and objects of theinvention, there is provided an electronically variable waveguide slotcoupler comprising a rectangular waveguide having a slot in a broadwallthereof, iris means including semiconductor elements disposed in thewaveguide transverse-ly from both sides of the slot, and control mean-sexternal to the waveguide and including a voltage source coupled to theelements for biasing the same to alter the current distribution ofenergy propagated through the waveguide and control the ratiation fromthe slot.

The following specifications and the accompanying drawings described andillustrate preferred embodiments of the present invention, likereference characters being used to designate like parts throughout thedrawings, wherein:

FIG. 1 is a perspective view, partially in section, showing oneembodiment of the iris controlled sl-ot coupler according to the presentinvention utilizing two irises formed from plate-like blocks ofsemiconductor material; and

FIG. 2 is a perspective view, partially in section, of anotherembodiment of the iris controlled slot coupler of the invention whereinvariable capacitance diodes are used to form the iris.

Referring now to the drawings, a portion of a standard rectangularwaveguide 10 is provided with a radiating centered slot 12 cut in abroadwell such as the upper broadwall 14-. In a first embodiment shownin FIG. 1, two fixed irises 26' and 20" of a first type aresymmetrically disposed in the waveguide 1.0 about the center of the slot12. In FIG. 2, another embodiment utilizing a single iris 40 of a secondtype is shown.

In FIG. 1, the irises 29' and 20" each include two spaced apartsemiconductor posts 22 and 24 and, when connected as described herein,each post behaves as a semiconductor diode. Each of the diode posts 22and 24 extend inwardly towards each other from the narrow walls 16 andare electrically grounded thereat to the waveguide 10. A metallizedlayer deposited on the ad' joining edge surface of each diode post formsa junction 26 and facilitates such an electrical connection.

A similar metallized layer forms a second junction 28 parallelling thejunction 26. The conductors 32 and 34, connected to and extending fromthe junctions 28, provide an electrical path for bias current to flowfrom a voltage source as for example, the voltage biasing network 39.The network 30 may include a battery 35 connected across thepotentiometers 36 and 37 each having movable taps 38 and 39 respectivelyconnected to the diode posts 24 at the junctions 28 thereof. Anintermediate terminal of the battery 35 may be grounded to the waveguide10 by a conductor 33.

A similar bias network, not shown, is also provided to bias the diodeposts 22 and is connected at the terminals 31h, 31b and 31c which, inall other respects, are analogous to the conductors 32, 33, and 34respectively.

With this bias arrangement, a variable electric field can beindependently established between the junctions 26 and 28 of each of thediode posts 22 and 24, by proper adjustment of the appropriatepotentiometers. However, it is necessary that the junctions 28 beelectrically insulated from the broadwalls 14 to prevent a short circuitof the bias voltage. This, for example, may be accomplished by theremoval of small outer end portions of the metallized layers forming thejunctions 28.

Thus, by controlling the bias voltage applied across each of the diodeposts 22 and 24, their microwave properties can be changed and in sodoing, the current distribution existing at the slot 12 is varied toeffect electronic control, in amplitude and phase, of the microwaveradiation emanating from the slot 12.

It should be pointed out that, where appropriate, a low frequencyalternating current generator, not shown, may be used in place of thebattery 35.

In FIG. 2, the iris 40 consists of two symmetrically disposed varactordiodes 42 and 44 lying in a transverse plane passing through the centerof the slot 12. One terminal of the diodes 42 and 44 is grounded to thewaveguide at the broadwall 14. The other terminal is connected to avoltage biasing network 50 by conductors 46 and 48 which terminate atthe movable taps 52 and 54 respectively of the potentiometers 56 and 58.A source of voltage, as for example, a battery 55 is connected acrossthe potentiometers 56 and 58 and, at an intermediate terminal 57, isalso grounded to the waveguide 10 by a conductor 60.

By biasing the varactor diodes 42 and 44 differentially, the electricalcharacteristics of one diode with respect to the other is varied anddistorts the current density in the vicinity of the slot 12 causing theslot coupling to change in a continuous fashion.

A conventional RF choke, as for example the commercially availablecoaxial choke 45, is provided in the biasing circuits for the varactordiodes 42 and 44 between each diode and its corresponding potentiometers52 and 54. With this arrangement, the diodes 42 and 44 may be biasedexternally to present a desired RF impedance to the RF energypropagating through the waveguide 10. At the same time, the RF chokespermit passage of a direct current, or a low frequency alternatingcurrent, for biasing the varactor diodes 42 and 44.

It should be pointed out that either one of the irises 20' and 20 may bedisposed in the waveguide 10 in a plane similar to the iris 40 of FIG.2; similarly, two irises of the type shown in FIG. 2 may be disposedrelative to the slot 12 as shown in FIG. 1. Moreover, the symmetricallydisposed iris 40 of FIG. 2 may be asymmetrically disposed either in thetransverse plane or in a plane passing transversely through the slot 12at other than its center.

By incorporating a single semiconductor iris, such as the iris 20 or theiris 40, transversely in a waveguide through the center of the radiatingslot, the amplitude of the slot radiation is variable as a function ofthe applied bias voltage. Adding another such iris and longitudinallydisplacing each from the slot center, the phase as well as the amplitudeis variable as a function of the bias voltage. With either one of theirises, 20' or 40, asymmetrically displaced relative to the slot center,the phase predominantly is variable as a function of the bias voltage.

For instance, in an iris controlled slot coupler of the type shown inFIG. 2, a 28 decibel range in amplitude control of slot radiation wasmeasured using the type 1N896 varactor diodes as manufactured by HughesAircraft Company. Each diode was spaced 0.176 inch from the narrow wallsof a standard X-band rectangular waveguide (i.e., diode separation of0.548). To achieve this coupling range, the diodes were biased forwardly0.31 volt for minimum slot coupling and, for maximum slot coupling, oneof the diodes is biased 5.0 volts while the other is held constant.Since the capacitance varies nonlinearly as a function of the biasvoltage applied across the varactor diode, a non-linear relationshipexists between the slot coupling and the differential bias voltageapplied to the diodes forming the iris.

It should be noted that although preferred, it is not essential that theiris or irises be symmetrically disposed in the Waveguide about itslongitudinal centerline or that the radiating slot be the shunt slot 12centrally positioned in the waveguide broadwall since, by proper biasingof the semiconductor irises, an asymmetrical iris or slot configurationmay in effect be made to appear symmetrical and vice versa to the RFenergy propagating through the waveguide and eventually coupled to theslot.

Thus, there has been shown and described an iris controlled slot couplerfor controlling the phase amplitude characteristics of the energyradiated from a slot. The resultant slot coupler is simple and compactin structure, light in weight and readily adaptable in new or existingslot and slot arrays regardless of the type or the slot groupconfiguration.

While only preferred embodiments of the invention have been set-forth,others may be made Without departing from the intended scope of theinvention, the purpose here being primarily descriptive and not limitingin any sense.

What is claimed is:

1. An electronically variable waveguide slot coupler comprising, arectangular waveguide having a slot in a broad wall thereof; iris meansincluding semiconductor elements disposed in said waveguide transverselyfrom both sides of said slot; and electrical control means external tosaid waveguide and including a voltage source electrically coupled tosaid elements for electrically biasing the same to alter the currentdistribution of energy propagated through said waveguide and controlradiation from said slot.

2. An electronically variable waveguide slot coupler comprising, arectangular waveguide having a slot in a broad wall thereof; iris meanssymmetrically mounted within said Waveguide in a plane extendingtransversely from said slot, said iris means including semiconductorelements; and electrical control means external to said waveguide andincluding a voltage source electrically coupled to said elements forelectrically biasing the same to alter the current distribution ofenergy propagated through said waveguide and control radiation from saidslot.

3. An electronically variable Waveguide slot coupler comprising, arectangular waveguide having a slot in a broad wall thereof; iris meanssymmetrically mounted within said waveguide in a transverse plane tosaid slot, said iris means including inductive elements ofsemiconductive material extending from the Walls of said waveguide; andelectrical control means external to said waveguide and including avoltage source electrically coupled to said elements for electricallybiasing the same to alter the current distribution of energy propagatedthrough said waveguide and control radiation from said slot.

4. An electronically variable waveguide slot coupler comprising, arectangular waveguide having a slot in a broad wall along thelongitudinal centerline thereof; iris means symmetrically mounted withinsaid waveguide in a transverse plane to said slot, said iris meansincluding inductive elements of semiconductive material ext ndinginwardly from the narrow walls of said waveguide; and control meansexternal to said waveguide and including a voltage source coupled tosaid elements for biasing the same differentially to alter the currentdistribution of energy propagated through said waveguide and controlradiation from said slot.

5. An electronically variable waveguide slot coupler comprising, arectangular Waveguide having a slot in a broad wall thereof; iris meanssymmetrically mounted within said waveguide in a plane extendingtransversely through said slot, said iris means including a pair ofplate-like inductive elements of semiconductive material extending inelectrical connecting relationship to and inwardly from the narrow wallsof said waveguide, each of said plate-like inductive elements having aninner edge surface disposed in a plane orthogonal to the broad wall anda conductive layer for forming a junction along said inner surface, saidlayer being electrically isolated from the broad walls of saidwaveguide; and electrical control means external to said waveguide andincluding a voltage source electrically coupled to each of said elementsfor biasing said plate-like inductive elements differentially to alterthe current distribution of energy propagated through said waveguide andcontrol radiation from said slot.

6. The slot coupler in accordance with claim 5 wherein said iris meansincludes'a first pair and a second pair of elements of semiconductivematerial each symmetrically disposed in spaced apart relationship fromthe longitudinal center of said slot.

7. An electronically variable waveguide slot coupler comprising, arectangular waveguide having a slot in a broad wall along thelongitudinal centerline thereof; iris means symmetrically mounted withinsaid Waveguide in a plane extending transversely through said slot, saidiris means including a pair of inductive elements of semiconductivematerial extending between the broad walls of said Waveguide, each ofsaid inductive elements being disposed in a plane orthogonal to thebroad walls and to the narrow walls of said waveguide; and electricalcontrol means external to said waveguide and including a voltage sourceelectrically coupled to each of said inductive elements for electricallybiasing said inductive elements differentially to alter the currentdistribution of energy propagated through said waveguide and controlradiation from said slot.

8. The slot coupler in accordance with claim 7 wherein said iris meansincludes a first pair and a second pair of elements of semiconductivematerial each symmetrically disposed in spaced apart relationship fromthe longitudinal center of said slot.

9. An electronically variable waveguide slot coupler comprising arectangular waveguide having a slot in a broad wall thereof; iris meansincluding semiconductor diode elements mounted within said Waveguide ina plane extending transversely to said slot; and electrical controlmeans external to said waveguide and including a voltage sourceelectrically coupled to said iris means for electrically biasing saidelements to alter the current distribution of energy propagated throughsaid waveguide and control radiation from said slot.

10. An electronically variable waveguide slot coupler comprising arectangular waveguide having a slot in a broad wall thereof; iris meansincluding semiconductor diodes having variable capacitancecharacteristics being transversely disposed Within said waveguide andadjacent either side of said slot; and electrical control means externalto said waveguide and including a voltage source electrically coupled tosaid iris means for electrically biasing said diode to alter the currentdistribution of energy propagated through said Waveguide and controlradiation from said slot.

11. An electronically variable Waveguide slot coupler comprising arectangular waveguide having a slot in a broad wall along thelongitudinal centerline thereof; iris means formed of capacitiveelements and including varactor diodes transversely mounted within saidwaveguide on both sides of said slot; and control means external to saidwaveguide and including a voltage source coupled to said iris means forbiasing said diodes to alter the current distribution of energypropagated through said waveguide and control radiation from said slot.

12. An electronically variable waveguide slot coupler comprising arectangular waveguide having a slot in a broad wall thereof; in's meansand including semiconductor diodes mounted in pairs Within saidwaveguide along both sides of said slot each said pair being mounted ina transverse plane that intersects the slot; and adjustable electricalcontrol means external to said waveguide and including a voltage sourceof low frequencies down to and including zero cycles per second forelectrically biasing said diodes and circuit means to form a lowimpedance path to the flow of current between said source and saiddiodes at the low frequencies, said circuit means concomittantly forminga high impedance path to substantially inhibit the flow of currenttherein at microwave frequencies so that the microwave currentdistributionof energy propagated through said waveguide is altered andthe slot radiation in amplitude and phase is a function of the biasselectively impressed across said diodes.

13. An electronically variable waveguide slot coupler comprising arectangular waveguide having a slot in a broad wall along the centerlinethereof; iris means formed of capacitive elements and including varactordiodes transversely mounted in pairs within said waveguide along bothsides of said slot; and adjustable control means external to saidwaveguide and including a voltage source of a low frequency includingzero for biasing said diodes and circuit means forming a low impedancepath to the flow of current at said low frequencies between said sourceand said diodes, said circuit means concomittantly forming a highimpedance path to substantially inhibit the flow of current therein atmicrowave frequencies so that the current distribution of energypropagated through said waveguide is altered and the slot radiation inamplitude and phase is a function of the bias selectively impressedacross said diodes.

14. An electronically variable waveguide slot coupler comprising arectangular waveguide having a slot in a broad wall along the centerlinethereof; iris means formed of capacitive elements and including varactordiodes symmetrically mounted in pairs within said waveguide in a planetransverse to said slot and passing through the center thereof; andadjustable control means external to said waveguide and including avoltage source of a low frequency including zero for biasing said diodesand circuit means forming a low impedance path to the flow of current atsaid low frequencies between said source and said diodes, said circuitmeans concomittantly forming a high impedance path to substantiallyinhibit the flow of current therein at microwave frequencies so that thecurrent distribution of energy propagated through said waveguide isaltered and the slot radiation in amplitude and phase is a function ofthe bias selectively impressed across said diodes.

15. An electronically variable waveguide slot coupler comprising arectangular waveguide having a slot in a broad wall along the centerlinethereof; iris means formed of capacitive elements and including varactordiodes symmetrically mounted in pairs within said waveguide in at leasttwo transverse planes each disposed longitudinally a predetermineddistance from the center of said slot; and adjustable control meansexternal to said waveguide and including a voltage source of a lowfrequency including zero for biasing said diodes and circuit meansforming a low impedance path to the flow of current at said lowfrequencies between said source and said diodes, said circuit meansconcomittantly forming a high impedance path to substantially inhibitthe flow of current therein at microwave frequencies so that the currentdistribution of energy propagated through said waveguide is altered andthe slot radiation in amplitude and phase is a function of the biasselectively impressed across said diodes.

16. An electronically variable waveguide slot coupler comprising arectangular waveguide having a slot in a broad wall along the centerlinethereof; iris means formed of capacitive elements and including varactordiodes asymmetrically mounted in pairs within said Waveguide in a planetransverse to said slot and passing through the center thereof; andadjustable control means external to said Waveguide and including avoltage source of a low frequency including Zero for biasing said diodesand circuit means forming a low impedance path to the flow of current atsaid low frequencies between said source and said diodes, said circuitmeans concomittantly forming a high impedance path to substantiallyinhibit the flow of current therein at microwave frequencies so that thecurrent distribution of energy propagated through said waveguide isaltered and the slot radiation in amplitude and phase is a function ofthe bias selectively impressed across said diodes.

17. An electronically variable waveguide slot coupler comprising arectangular waveguide having a slot in a broad wall along the centerlinethereof; iris means formed of capacitive elements and including varactordiodes asymmetrically mounted in pairs within said waveguide in at leasttwo transverse planes each disposed longitudinally a predetermineddistance from the center of said slot; and adjustable control meansexternal to said waveguide and including a voltage source of a lowfrequency including zero for biasing said diodes and circuit meansforming a low impedance path to the flow of current at said lowfrequencies between said source and said diodes, said circuit meansconcomittantly forming a high impedance path to substantially inhibitthe flow of current therein at microwave frequencies so that the currentdistribution of energy propagated through said waveguide is altered andthe slot radiation in amplitude and phase is a function of the biasselectively impressed across said diodes.

18. An electronically variable waveguide slot coupler comprising arectangular waveguide having a slot in a broad wall along a lineparallel to and spaced from the centerline thereof; iris means includingsemiconductor diodes transversely mounted in pairs within said waveguidealong -both sides of said slot and symmetrically therewith; andadjustable electrical control means external to said waveguide andincluding a voltage source of low frequencies down to and including zerofrequency for biasing said diodes, and circuit means forming a lowimpedance path to the flow of current at said low frequencies betweensaid source and said diodes, said circuit means concomittantly forming ahigh impedance path to substantially inhibit the flow of current thereinat microwave frequencies so that the current distribution of microwaveenergy propagated through said waveguide is alteredand the slotradiation in amplitude and phase is a function of the electrical biasselectively impressed across said diodes.

19. The slot coupler in accordance With claim 18 wherein each said irismeans comprises two semiconductor diodes disposed in a transverse planesymmetrically about the oil-centered slot, said plane beinglongitudinally disposed along said slot a predetermined distance fromthe center thereof.

References Cited by the Examiner UNITED STATES PATENTS 7/1960 Shanks343-768 OTHER REFERENCES HERMAN KARL SAALBACH, Primary Examiner.

E. LIEBERMAN, W. K. TAYLOR,

Assistant Examiners.

1. AN ELECTRONICALLY VARIABLE WAVEGUIDE SLOT COUPLER COMPRISING, ARECTANGULAR WAVEGUIDE HAVING A SLOT IN A BROAD WALL THEREOF; IRIS MEANSINCLUDING SEMICONDUCTOR ELEMENTS DISPOSED IN SAID WAVEGUIDE TRANSVERSELYFROM BOTH SIDES OF SAID SLOT; AND ELECTRICAL CONTROL MEANS EXTERNAL TOSAID WAVEGUIDE AND INCLUDING A VOLTAGE SOURCE ELECTRICALLY COUPLED TOSAID ELEMENTS FOR ELECTRICALLY BIASING THE SAME TO ALTER THE CURRENTDISTRIBUTION OF ENERGY PROPAGATED THROUGH SAID WAVEGUIDE AND CONTROLRADIATION FROM SAID SLOT.